mediaproxy performance

I am using openser + mediaproxy.  From the top, I found the the CPU
usage is increased when the number of sessions increased.  When the
system handling 30 current sessions, the CPU usage is occupied by
python on 80%.  When the system handling 40 current sessions, the CPU
usage is occupied by python over 90% and the system is hanged somehow.
As I know, mediaproxy is written by python.  That's mean mediaproxy
uses much CPU resource for handling RTP session.  Is it the real case
of using mediaproxy?  If I want to handle more RTP session, what can I
do (use rtpproxy)?

Thanks!